1. Field of the Invention
This invention relates to an improved apparatus and method of the shuttle blow molding type, which is also referred to as the extrusion blow molding type, for producing thermoplastic containers. More particularly, this invention relates to an improved apparatus and method of the foregoing character for removing the moil portion of a thermoplastic container during its production by shuttle blow molding or extrusion blow molding.
2. Description of the Prior Art
In the production of thermoplastic containers by extrusion blow molding, a blow pin is reciprocated relative to a blow mold to inject blowing air into the container being formed in the blow mold from an extruded tubular parison of thermoplastic material that is at an elevated temperature. Blowing air is introduced into the parison through the blow pin when the free end of the blow pin is positioned within the parison, and the blow pin is thereafter removed from the blow mold to permit the blown container therein to be removed from the mold.
The molding equipment used in producing a plastic container by shuttle blow molding includes a body mold in which the body portion of the container is formed by blowing and a finish portion of the container is blown in a separate annular neck mold that is positioned at an open end of the body mold. The body mold and the neck mold are each made up of a separable pair of mold halves, and are normally opened and closed in unison, though the neck mold may be separately removed from the body mold, for example, to replace it with a different neck mold if required to produce a container with a finish that is different in size or type. Before removal of the blown container from the molding equipment, the halves of the body mold and the neck mold are separated, and takeout tooling is inserted into the finish of the blown container to remove the blown container from the molding equipment. In the production of blown plastic containers according to the shuttle blow molding process, an axially and radially outwardly projecting annular scrap portion, which is usually referred to a moil, is formed at the rim of the container, and this moil must be severed from the container and then appropriately discarded before the container is ready for shipment to a packing plant. The severing of the moil is usually done by a cutter portion of the blow pin that compresses the moil in a thin annular pattern against an anvil portion of the neck mold. However, the severing and the appropriate discarding of the moils from shuttle blow molded thermoplastic containers heretofore was difficult to control because the tendency of the moils to adhere to the blow pin and to disengage from the container in an uncontrolled manner as the blow pin was extracted from the molding equipment.
According to the present invention, a moil at the rim of a container produced by shuttle blow molding is controllably removed from the container by providing the neck mold with a moil retaining tool element against an anvil that is used to prevent impact damage between the blow pin and the neck mold, and to cut the moil from the container. The moil retaining tool element is annular in configuration, and has a radially inwardly projecting annular flange that projects into the moil and positively retains the moil in position at the rim of the container as the blow pin is removed from the mold equipment, and notwithstanding the tendency of the moil to adhere to the blow pin. Thereafter, before or after the parting of the halves of the molding equipment the takeout tooling that is used to remove the container from the body mold is inserted into the container through the finish and is then extracted, after the opening of the molding equipment thereby removing the container and moil, in unison, from the body mold. Subsequently, the takeout tooling is used to transfer the container and moil to a separate station, at a controlled location and time in the production cycle, at which the moil and the container are separately discharged, and the takeout tooling is returned to the mold equipment to begin a repeat of the foregoing cycle.
Accordingly, it is an object of the present invention to provide an improved apparatus and method for producing thermoplastic containers by extrusion blow molding. More particularly, it is an object of the present invention to provide an apparatus and method of the foregoing type in which the moils produced at the rims of such containers are positively retained in engagement with the rims of the containers during the removal of the blow pin from the molding equipment and are thereafter severed from the containers in a controlled manner.
For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following brief description thereof, to the detailed description of the preferred embodiment and to the appended claims.